The present invention relates to a process for forming and installing an electrical heater which is capable of heating a long interval of subterranean earth formation and, where desired, is arranged to facilitate the temperature logging of the heated zone through a thermal well conduit extending from a surface location to the interval being heated.
It is known that benefits can be obtained by heating intervals of subterranean earth formations to relatively high temperatures for relatively long times. Such benefits may include the pyrolyzing of an oil shale formation, the consolidating of unconsolidated reservoir formations, the formation of large electrically conductive carbonized zones capable of operating as electrodes within reservoir formations, the thermal displacement of hydrocarbons derived from oils or tars into production locations, etc. Prior processes for accomplishing such results are contained in patents such as the following, all of which are U.S. patents. U.S. Pat. No. 2,732,195 describes heating intervals of 20 to 30 meters within subterranean oil shales to temperatures of 500.degree. to 1000.degree. C. with an electrical heater having iron or reusable chromium alloy resistors. U.S. Pat. No. 2,781,851 by G. A. Smith describes using a mineral-insulated and copper-sheathed low resistance heater cable containing three copper conductors at temperatures up to 250.degree. C. for preventing hydrate formation, during gas production, with that heater being mechanically supported by steel bands and surrounded by an oil bath for preventing corrosion. U.S. Pat. No. 3,104,705 describes consolidating reservoir sands by heating residual hydrocarbons within them until the hydrocarbons solidify, with "any heater capable of generating sufficient heat" and indicates that an unspecified type of an electrical heater was operated for 25 hours at 1570.degree. F. U.S. Pat. No. 3,131,763 describes an electrical heater for initiating an underground combustion reaction within a reservoir and describes a heater with resistance wire helixes threaded through insulators and arranged for heating fluids, such as air, being injected into a reservoir. U.S. Pat. No. 4,415,034 describes a process for forming a coked-zone electrode in an oil-containing reservoir formation by heating fluids in an uncased borehole at a temperature of up to 1500.degree. F. for as long as 12 months.
Various temperature measuring processes have been described in patents. U.S. Pat. No. 2,676,489 describes measuring both the temperature gradient and differential at locations along a vertical line in order to locate the tops of zones of setting cement. U.S. Pat. No. 3,026,940 discloses the need for heating wells for removing paraffin or asphalt or stimulating oil production and discloses the importance of knowing and controlling the temperature around the heater. It describes a surface located heater that heats portions of oil being heated by a subsurface heater, with the extent of the heater control needed to obtain the desired temperature at the surface located heater being applied to the subsurface heater.
Various temperature measuring systems involving distinctly different types of sensing and indicating means for uses in wells have also been described in U.S. patents. For example, patents such as Nos. 2,099,687; 3,487,690; 3,540,279; 3,609,731; 3,595,082 and 3,633,423 describe acoustic thermometer means for measuring temperature by its effect on a travel time of acoustic impulses through solid materials such as steel. U.S. Pat. No. 4,430,974 describes a measuring system for use in wells comprising contacting a plurality of long electrical resistant elements (grouted in place) with a scanner for sequentially connecting a resistance measuring unit to each of the resistance elements. U.S. Pat. No. 3,090,233 describes a means for measuring temperatures within small reaction zones such as those used in pilot plants. A chain drive mechanism pushes and pulls a measuring means such as a thermocouple into and out of a tube extending into the reaction zone while indications are provided of the temperature and position within the tube.